Traveling matte photographic processes enable the foreground and background portions of a motion picture scene to be photographed separately and then combined to produce a single composite image. This process can have many practical advantages. It permits sharp focus of both foreground and background, permits separate control of the color balance for foreground and background, and facilitates many special effects that could not otherwise be produced. It can also contribute markedly to production efficiency since the two component parts of a scene can be photographed at different times and in different places.
The essence of traveling matte photography, from a technical point of view, is the production of a silhouette or "matte" of the foreground component of the scene. This matte is used to prevent exposure of the corresponding portion of a film while the background is recorded. The foreground is added later on the unexposed portion of the film, as explained in U.S. Pat. No. 3,158,477 to Vlahos.
To produce such a matte by conventional techniques, the foreground, which is usually an action scene, is staged first in front of a plain backing referred to herein as a screen. This type of system is commonly known as a "blue screen" system because blue is the color usually chosen for the screen. Blue is preferred because, as compared to the other primary colors, it has less intensity in flesh tones and can therefore be more completely eliminated from a typical foreground scene.
The foreground is photographed before the blue screen using a color negative film. The blue component of this negative is then separated by a series of steps, employing filters and high contrast film techniques, to ultimately produce a matte that is dense in the foreground areas and transparent in blue screen areas.
A number of variations of this "blue-screen" system are used but they all generally employ the same basic known principles. The fundamental problem with all such systems is the achievement of accuracy in the matte which must precisely fit the foreground portion of the scene. Accuracy is lost primarily due to the need to reprint the image at least three times, and sometimes more often, before the desired matte is ultimately produced. During this process the matte image tends to grow and the fine details of its outline are lost. A matte that is too large will result in a composite image that includes a black "matte line" surrounding the foreground. A matte that is too small, which is less common, will produce "fringing", i.e., the foreground is surrounded by a thin border of bright light.
Another problem associated with conventional blue screen systems is that the production of the matte, with many intermediate steps, tends to be a time consuming and labor intensive process and is therefore costly.
An objective of the present invention is the production of a matte by a simplified process that eliminates many intermediate steps, producing a high quality and more accurate matte at a lower cost. Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.